When I had to start the Second Levelling of Finland, 43 years ago, after the first observing summer I made one important and happy finding. The vibration of the image in the levelling instrument made the levelling difficult in middle summer while in spring and autumn this trouble was not so bad. So I proposed that levelling work must be interrupted for the six weeks from the midsummer to the beginning of August and that was accepted. The fact that just these weeks are the best vacation time in Finland made our colleagues in the institute jealous, but it was not our fault, and we were happy.